Question

Consider this case class:

case class IntPrinter(implicit val i: Int) {
  def print()(implicit i: Int) = println(i)
}

I can instance it explicitly passing a value for the implicit argument like this:

val p = IntPrinter()(9)

I’ve been told in IRC that, from now on, the explicitly passed value will be implicitly passed to print when being called, but that’s not the case:

p.print()
 error: could not find implicit value for parameter i: Int

Am I doing something wrong or I’ve misunderstood/been given incorrect information? Is there any way to achieve this?

---

EDIT: as a matter of fact it works as expected if I import p._ like this:

import p._
p.print()

Which indeed prints 9.

Is this the correct behaviour? Is using import as bad idea as it sounds? How do I workaround this?

Answer 1

Indeed it’s the correct behaviour. implicit values are only searched in current scope and calling print outside IntPrinter means it’s not on the class scope (obviously) and the reason why I had to import it.

The correct way to do what I wanted:

case class IntPrinter(implicit val i: Int) {
  def print()(implicit i: Int) = println(i)
  def printProxy() = print()
}

And then calling p.printProxy behaves like I wanted it to behave (because printProxy is inside IntPrinter‘s scope.)